This application relates to Japanese Patent Application No. Hei. 10-214493 filed Jul. 29, 1998, the entire contents of which are incorporated herein by reference.
1. Field of the Invention
The present invention relates to a cooling apparatus for a liquid-cooled internal combustion engine, such as a water-cooled engine, and it is preferably applicable to an internal combustion engine of a vehicle.
2. Description of Related Art
It is necessary to keep the engine cooling water temperature appropriate in order to drive the engine efficiently.
One type of known cooling apparatus for an engine is disclosed in JP-A-63-268912. The cooling apparatus disclosed in JP-A-63-268912 controls the engine cooling water temperature based on a wall surface temperature of the cylinder block of the engine.
In order to appropriately control the engine cooling water temperature at a cooling water inlet of an engine, the inventors of the present invention tried to develop a cooling apparatus having a flow control valve, at a connection between a radiator outlet side and a bypass passage which bypasses the radiator, which controls a flow rate of a radiator and a flow rate of the bypass passage. Further, the inventors tried to feedback control the valve opening degree of the flow control valve based on the cooling water temperature at a cooling water inlet side of the engine (cooling water inlet side of a pump). However, it was difficult to accurately control the cooling water temperature at the cooling water inlet side of the engine (hereinafter referred to as xe2x80x9cthe inlet temperaturexe2x80x9d) because of the following reason.
The inlet temperature is determined based on the temperature and the flow rate of the cooling water flowing out from the radiator and the temperature and the flow rate of the cooling water flowing out from the bypass passage. On the other hand, the inventors"" experimental model controls the valve opening degree based on only the temperature, regardless of the flow rate.
Accordingly, the change of the flow rate caused by the change of the valve opening amount is not reflected to the control of the flow control valve, and the control accuracy of the inlet temperature is compromised.
To solve this problem, it is possible to detect the flow rates of the cooling water flowing out from the radiator and the cooling water passed through the bypass passage, and to add the detected flow rates to the control parameters. However, it is practically difficult to place a flow rate detector, sensor and the line in the engine room because of the mounting space and the cost thereof.
The present invention is made in light of the above-mentioned problem, and it is an object of the present invention to provide a cooling apparatus which improves the control accuracy of the inlet temperature without detecting the flow rate of the cooling water.
According to a cooling apparatus of the present invention, an opening degree of a flow control; valve is controlled based on a first temperature (Tp) of the coolant discharged from an outlet of the flow control valve, a second temperature (Tb) of the coolant flowing through a bypass passage, and a third temperature (Tr) of the coolant flowing out from a radiator.
Accordingly, the cooling water temperature at the inlet of the engine is accurately controlled since the flow control valve is controlled by parameters including the flow rate without detecting the flow rate of the cooling water.